It should be noted that trans fat values must be interpreted with caution because many fast food establishments, restaurants and industries may have changed the type of fat used for frying and cooking since the analysis were done (e.g. on July 1, 2008 in New York trans fats are banned in its 40.000 restaurants).

Foods with trans fats: margarine

Fig. 1 – Margarine

Among foods with trans fats, stick or hard margarine had the highest percentage of them, but levels of these fatty acids have declined as improved technology allowed the production of softer margarines which have become popular. But there are difference in trans fat content of margarine from different country:

the greatest contents are found in soft margarine from Iceland, Norway, and the UK (13-16,5% of total fatty acids);

less contents are found in Italy, Germany, Finland, and Greece (5.1%, 4.8%, 3.2%, and 2.9% of total fatty acids, respectively);

in Portugal, The Netherlands, Belgium, Denmark, France, Spain, and Sweden margarine trans fat contents are less than 2% of the total fatty acids.

USA and Canada lag behind Europe, but with advent of trans fat labeling of foods in USA change is occurring. For this reason, at now, in USA margarine is considered to be only a minor contributor of the total trans fats, whereas the major sources are commercially baked and fast food products like cake, cookies, wafer, snack crackers, chicken nuggets, French fries or microwave-oven popcorn (see below).

Foods with trans fats: shortenings

Trans fat content of shortening ranges from 6% to 50% and varies in different country: in Germany, Austria and New Zealand it is less than France or USA.
However like margarines, trans fat content of shortenings is decreasing; i.e. in German shortenings it decreased from 12% of total fatty acids in 1994 to 6% in 1999, in Denmark is 7% (1996) while in New Zealand is about 6% (1997).

Foods with trans fats: vegetable oils

At now, nonhydrogenated vegetable oils for salad and cooking contain no or only small amounts of trans fats. Processing of these oils can produce minimal level of them ranged from 0.05g/100 g food for extra virgin oil to 2,42 g/100 g food for canola oil. So their contribution to trans fat content to the current food supply is very little.
One exception is represented by Pakistani hydrogenated vegetable oils (vegetable ghee/vanaspati) whose trans fat content range from 14% to 34% of total fatty acids.

Foods with trans fats: prepared soups

Among foods with trans fats, prepared soups contain significant amount of them, ranging from 10% of beef bouillon to 35% of onion cream; so they contribute great amount of trans fats to the diet if frequently consumed.

Foods with trans fats: processed foods

Thanks to their long shelf life as their flavor stability, trans fats are used in many processed foods as cookies, cakes, croissants, pastries and other baked goods.
Baked goods are the greatest source of these fats in North American diet. Of course, their trans fat contents depend on the type of fat used in processing. In USA after 2006, when labeling laws were implemented, many processed foods have been reformulated and contain less than 0,5 g of industrial trans fats per serving; so producers can list their content as 0 on the packaging, but it‘s not 0!

Foods with trans fats: sauces

Mayonnaise, salad dressings and other sauces contribute only small or no-amounts of trans fats to the diet.

Foods with trans fats: human milk and infant foods

Trans fat content of human milk reflects the trans fatty acid content of maternal diet in the previous day. In human milk it comprise 1%-7% of the total fatty acids but decreasing from 7.1 in 1998 to 4.6 in 2005/2006.Infant formulas have trans fat values on average 0.1%-4.5% with a brand up to 15.7% of the total fatty acids.
Baby foods contain greater than 5% of trans fats.

Foods with trans fats in fast foods and restaurants

Fig. 2 – French Fries

Shortenings with high amounts of trans fats are used as frying fats, so fast foods and many restaurant’s foods may contain relatively large amounts of them.
Foods with trans fats are fried pies, French fries, chicken nuggets, hamburgers, fried fish as well as fried chicken.
For French fries and chicken nuggets their content varies largely from nation to nation, but also within the same fast food chain in the same country because of the cooking oil used. For example oil used in USA and Peru outlets of a famous fast food chain contains 23-24% of trans fats, whereas oil used in many European countries of the same fast food chain contains about 10% trans fats, with some countries as low as 5% and 1% (Denmark).
On 2006, Stender et al. reported that a meal of French fries and chicken nuggets purchased at McDonald ‘s in New York City contained over 10 g of trans fats, while if purchased at Kentucky Fried Chicken in Hungary they are almost 25 g.
Again, from the work of Stender et all. it can see a cross-country comparison of trans fat contents of chicken nuggets and French fries purchased at McDonald ‘s or Kentucky Fried Chicken: trans fat contents vary depending on the country and even the city and often in the same city.

In industrialized countries, greater part of the consumed trans fatty acids are produced industrially (in USA about 80%), in varying amounts, during partial hydrogenation of edible oils containing unsaturated fatty acids.
Hydrogenate means to add hydrogen atoms to unsaturated sites (that is, on a double bond) on the carbon chains of fatty acids by heating vegetable oils in presence of metal catalyst and hydrogen.
During the partial hydrogenation, an incomplete saturation of the unsaturated sites on the carbon chains of unsaturated fatty acids occurs: some double bonds remain, but they may be moved in their positions on the carbon chain, producing geometrical and positional isomers (double bonds are modified in both conformation and position).
Notably, with regard to fish oil, trans fatty acid content in non-hydrogenated oils and in highly hydrogenated oils is 0,5 and 3,6%, whereas in partially hydrogenated oils is 30%.
Hydrogenation converts vegetable oils into semisolid fats for use in:

moreover, they are positively associated with the risk of coronary heart disease (CHD), and sudden death from cardiac causes and diabetes.

Industrial trans fatty acids are an independent cardiovascular risk factor.
Their adverse effects are seen at low level of intake: for a person consuming 2000 kcal/d, 20-60 kcal from industrial trans fatty acids, equivalent to about 2-7 g or 1-3% of the total energy intake, is enough.So, avoidance of industrial trans fatty acids, or a consumption of less 0,5% of total daily energy intake is necessary to avoid their adverse effects (these are far stronger, on average, than those of food contaminants or pesticide residues!).

Dietary trans fatty acids from deodorization of vegetable oils

Very small amounts of trans fatty acids (less than 2 percent) are formed during deodorization of vegetable oils, a process unrelated to partial hydrogenation and necessary in the refining of edible oils. During this process trans fatty acids with more than one double bond are formed in small amounts (if the isomer contains 18 carbon atoms it is marked C18:2). These isomers are also present in fried foods and in considerable amounts in partially hydrogenated vegetable oils (e.g. soybean oil).

Dietary trans fatty acids from animals

A natural source comes from bacterial transformation of a proportion of the relatively small amounts of unsaturated fatty acids ingested by ruminants in their rumen.
They are present at low levels in meat and full fat dairy products from cows, sheep, and other ruminants (typically <5% of total fatty acids).

Dietary trans fatty acids from vegetables

Another natural source is represented by some plant species, and plant-derived foods as:

“Homemade”dietary trans fatty acids

Isomers of dietary trans fatty acids

Fig. 2 – ITFA

The most important cluster of trans fatty acids both animal and industrial origin is isomers containing 18 carbon atoms plus one double bond (C18:1) whose position varies between the Δ6 and Δ16 carbon atoms of molecule.
Even if the same trans fatty acids are largely present in industrial trans fatty acids and in trans fatty acids from ruminants, there is a considerable quantitative difference between individual molecules in the two different sources.
The most common isomers in both sources are those with double bond in position between Δ9 and Δ11, but Δ11-C18:1 or vaccenic acid represents over 60% of the trans C18:1 isomers in ruminant trans fatty acids, whereas in industrial ones Δ9-C18:1 or elaidic acid comprises 15-20%, and Δ10-C18:1 and Δ11-C18:1 over 20% each others.

some plant species like leeks, peas, lettuce, spinach and rapeseed oil (small amounts).

In industrialized countries, the greater part of the consumed trans fatty acids are produced industrially, in varying amounts, during partial hydrogenation of edible oils containing monounsaturated and polyunsaturated fatty acids.
Note: partially hydrogenated vegetable oils were developed in the United States in 1903 as a cheaper alternative to animal fats.

While ruminant trans fatty acids, in amounts actually consumed in diets, are not harmful for human health, consumption of industrial partially hydrogenated fatty acids has neither apparent benefit nor intrinsic value, above their caloric contribution: from human health standpoint they are only harmful.

Chemical structure of trans fatty acids

Fatty acids

Fatty acids are made up by carbon (from the “smallest”, formic acid, containing only one carbon atom, up to fatty acids with over 30 carbon atoms), hydrogen and oxygen atoms linked to form a carboxylic group (the “hydrophilic head” of the molecule) that continues in a more or less long chain of carbon atoms linked each other by chemical bonds that may be single or double (the “hydrophobic tail”). Hydrogen atoms are linked to carbon and oxygen atoms.Fatty acids are defined:

saturated, if chemical bonds between carbon atoms of the chain are all simple;

Cis and trans isomers

Fig. 1 – Cis and Trans Isomers

Carbon-carbon double bonds show planar conformation and so they can be considered as plans whose opposite sides carbon chain attaches and continues.
“The entry” and “the exit” of the carbon chain from the plain may occur on the same side of the plan, and in this case double bond is defined in cis configuration, or on opposite side, and in that case it is defined in trans configuration.Unsaturated fatty acids most commonly have their double bonds in cis configuration; the other, less common, configuration is trans.Unsaturated fatty acids with at least one double bond in trans configuration are called trans fatty acids.Cis bond causes a bend in the fatty acids chain, whereas the geometry of trans bond straightens the fatty acid chain, imparting a structure more similar to that of saturated fatty acids.
Bent molecules can’t pack together easily but linear ones can do it and this gives the fats in which they are a higher melting point. Heightening the melting point of fats means that it is possible to convert them from liquid form to semi-solids and solids; for this reason fats containing a greater part of saturated fatty acids, or the geometrically similar partially hydrogenated fatty acids, are solid at room temperature (partially hydrogenated fatty acids tend to be less solid than saturated fats).

In industrially trans fatty acids-containing fats, cyclic monomers as well as intramolecular linear dimmers are also present.

Fat and protein intake and risk of non-Hodgkin lymphoma

In a clinic-based study published on Journal of Nutrition a research team evaluated the association of dietary fat and protein intake with risk of non-Hodgkin lymphoma in 603 cases (105 diffuse large B-cell lymphoma, 146 follicular lymphoma, and 218 chronic lymphocytic leukemia/small lymphocytic lymphoma) and 1007 frequency-matched controls.

Fig. 1 – Trans Fat Cartoon

While omega-3 fatty acid intake was inversely associated with non-Hodgkin lymphoma risk, trans fatty acid intake was positively associated with risk and there was no association with total, animal, plant-based, or saturated fat intake.
When examining intake of specific foods, fresh fish and total seafood intakes were inversely associated with risk, whereas intakes of processed meat, milk containing any fat, and high-fat ice cream intakes were positively associated with risk.

In conclusion, the study showed that diets high in omega-3 fatty acids and total seafood were inversely associated with non-Hodgkin lymphoma risk, whereas diets high in trans fatty acids, processed meats, and higher fat dairy products were positively associated with risk.

The hydrogenation of vegetable oils

The process of hydrogenation was first discovered in 1897 by French Nobel prize in Chemistry (jointly with fellow Frenchman Victor Grignard) Paul Sabatier using a nickel catalyst.Partially hydrogenated vegetable oils were developed in 1903 by a German chemist, Wilhelm Normann who files British patent on “Process for converting unsaturated fatty acids or their glycerides into saturated compounds” and the term trans fatty acids or trans fats (they are produced during partial hydrogenation of edible oils containing monounsaturated and polyunsaturated fatty acids) appeared for the first time in the Remark column of the 5th edition of the “Standard Tables of Food Composition” in Japan.

contribute to the hardness of fat in which they are who can be semi-solids and solids (they are used to make margarine or shortening with a melting point, consistency and “mouth feel” similar to those of butter);

The war on artificial trans fats

Fig. 1 – Shortening

The first hydrogenated oil was cottonseed oil in USA in 1911 to produce vegetable shortening.
So, before this date, the only trans fats in human diet were those derived from ruminants.
In the 1930’s partial hydrogenation became popular with the development of margarine; through hydrogenation, oils such as soybean, safflower and cottonseed oil, which are rich in unsaturated fatty acids, are converted to margarines and vegetable shortenings.
Until 1985 no adverse effects of trans fats on human health was demonstrated and in 1975 Procter & Gamble study shows no effect of partially hydrogenated fats on cholesterol.
Their use in fast food preparation grow up from 1980’s when the role of dietary saturated fats in increasing cardiac risk began clear; it was led a successful campaign to get McDonald’s to switch from beef tallow to vegetable oil for frying its French fries. Meanwhile, studies began to raise concerns about their effects on health: on 1985 in USA Food and Drug Administration (FDA) concludes that trans fats and monounsaturated fat oleic acid affect serum cholesterol level similarly but from the second half of 1985 their harmful began clear and the final proof comes from both controlled feeding trials and prospective epidemiologic studies.
After June 1996 they were eliminated from margarine sold in Australia, which before contributed about 50% of the dietary intake of trans fatty acids in such country.
On March 11, 2003 the Danish government, after a debate started in 1994 and two new reports in 2001 and 2003, decided to phase out the use of industrially produced trans fats(ITFA) in food before the end of 2003; two years later, however, the European Commission asked Denmark to withdraw this law, which was not accepted on the EU level, unfortunately.
Canada is considering legislation to eliminate industrially produced trans fats from food supplies.
On 2003 FDA ruled that food labels (for conventional foods and supplements) show trans fat content beginning January 1, 2006. Notably, this ruling is the first substantive change to food labeling since the requirement for per-serving food labels information was added in 1990.
On 2005 the US Department of Agriculture made a minimized intake of trans fats a key recommendation of the new food-pyramid guidelines.
On 2006 American Heart Association recommends to limit their intake to 1% of daily calorie consumption and suggests food manufacturers and restaurants switch to other fats.
On 2006 New York City Board of Health announces trans fat ban in its 40.000 restaurants within July 1, 2008.